1. Field of the Invention
The invention refers to a method for quality control for two-dimensional matrix codes on metallic workpieces, which are present in the form of embossed marking dots, with an image processing device.
2. The Related Art
The marking dots of such a two-dimensional matrix code are normally embossed by means of a hard-metal needle of a marking tool. This is done on one hand very fast and on the other hand in a very narrow arrangement, wherein such matrix areas can be very small and possess a length and width of only a few millimeters. For being able to read back the information of the matrix code without any errors, the precision in placing the marking dots is of high importance, with the exact shape, size, position and depth of the marking dots being important quality features. It is therefore very critical to check, during or after the production of such a matrix code, whether the information can be read back without any errors, i.e. whether the marking dots are present in the correct place in the necessary quality.
Known methods for the quality control of two-dimensional matrix codes use a “finder function” like the one which is used at reading for the position determination of the code array. The square matrix codes have two adjacent outlines with marking dots in narrow sequence. These two outlines are searched in the image data collected by a camera as an image processing device for determining the position of the matrix code in this manner. The two other outlines have marking dots whose distance corresponds, respectively, to the distance of the grid lines of a grid possessing the marking dots as grid points. Thus, these grid points are determined from the image data and, subsequently, the calculated points are checked as to whether a marking dot of the desired quality is positioned there. Due to image capture, image processing and subsequent calculation, multiple error factors are included in quality control which render the entire process very imprecise, in particular in case of very small distances between the dots.